Lecture Autodesk inventor Orthographic projections

Orthographic Projections


Orthographic Projections
Parallel projection technique
Projectors normal to projection plane
Projection Plane

Projectors
NOTE: CAD Systems typically use orthographic projection


Orthographic Projection Categories
Axonometric



Three object faces visible
No principal axes
parallel/perpendicular to
projection plane

Multiview




Only one object face
visible
One object face (i.e., two
principal axes) parallel to

projection plane


Axonometric Projections
Classed according to angles made by principal axes
when projected onto projection plane
Trimetric – no equal angles
 All principal axes foreshortened unequally
Dimetric – two angles are equal
 Two principal axes are equally
foreshortened
Isometric – all angles equal (iso  equal,
metric  measure)
 All principal axes foreshortened equally


Axonometric Projection Classes


Isometric Scaling
Lines parallel to any
principal axis are
foreshortened equally
( scaled proportionally)
Measurements can be
made parallel to any of
the three principal axes

NOTE: In a trimetric projection, measurements along a given
principal axis are proportional; however, measurements along

different principal axes are not scalable


Isometric Projections
All 3 principal axes equally foreshortened 
same scale
Can be visualized as looking down the diagonal
of a cube

Trimetric Projection Isometric Projection


Isometric Drawings
It can be shown that, in an isometric projection:
Each axis is foreshortened
to approximately 82% of its
true length
To correct for this, an
isometric projection can be
plotted at a scale of 1/.82
(~1.22). This convenient
approximation of an
isometric projection is called
an isometric drawing


Isometric Viewing
An isometric projection is obtained by rotating
the view:
About a vertical axis (45 ± 90n)º (n is an

integer), then
Out of the horizontal plane, ±35.26º

Front

Front, Side

Top, Front, Side


Isometric Sketching
In sketching an isometric view, principal axes
are aligned as shown below:


Orthographic Projections